Specify pressure and olivine, spinel and orthopyroxene compositions:
Leave input temperature set to zero to calculate a temperature from olvine-spinel equilibrium and a log10 fO2 from olvine-spinel-orthopyroxene equilibrium. Alternately, input a temperature to calculate a log10 fO2 from olvine-spinel-orthopyroxene metastable exchange equilibrium at the specified temperature and pressure.